A relay is an automatic switch device having isolation function, widely applied in communication, automobiles, automatic control, household appliances and other fields, and is one of the most important control devices.
Due to demands in energy preservation and environment protection, magnetic latching relays are applied to ever wide areas. Common relays require to be developed with magnetic latching features. Generally, for a typical clap-type relay, an iron core (or an iron yoke) is divided into two parts. A permanent magnet is connected between the two parts, to form a series-type magnetic circuit. Upon excitation of a coil, the magnetic circuit is closed, and a magnetic force generated by the permanent magnet can keep an armature in closed state. FIG. 1 is a schematic structural diagram of a magnetic circuit of a magnetic-latching-type electromagnet relay in the prior art. As shown in FIG. 1, the magnetic circuit of the electromagnet relay includes a spring sheet 101 (which can form a part of an output circuit of the relay), an armature 102, an iron yoke 103, an iron core 104, a coil 105 and a permanent magnet 106. The iron core 104 passes through the coil 105. The permanent magnet 106 is fixed between the iron core 104 and the iron yoke 103. The armature 102 and the spring sheet 101 are riveted together in advance, and riveted onto the iron yoke 103. The permanent magnet 106 generates a permanent magnetic circuit which starts from an N pole of the permanent magnet, passes through the iron core 104, an air gap, the armature 102, the iron yoke 103, reaches an S pole of the permanent magnet. Upon excitation, the coil 105 generates a magnetic field which passes through the iron core 104, the air gap, the armature 102, the iron yoke 103 and the S-N of the permanent magnet. When the permanent magnet filed and the magnetic field generated by the coil is in the same direction, the magnetic forces will add to each other to form a force which overcomes the counter force of the spring sheet 101, so as to cause the armature 102 and the iron core 104 to attract each other. After the excitation of the coil 105 stops, the magnetic field generated by the coil will disappear, and the permanent magnetic field will provide a retention force to keep the armature 102 and the iron core 104 in the attracted state. When a reverse current flows through the coil, the coil 105 generates a magnetic field which passes through the iron core 104, the N-S of the permanent magnet, the iron yoke 103 and the armature 102. Thus, the magnetic field generated by the coil is opposite to the direction of the permanent magnetic field, and weakens the permanent magnetic force. Under the “cooperation” of the counter force of the spring sheet 101, the spring sheet 101 brings the armature 102 to be reset.
Such a series-type magnetic circuit has the following defects.
1. The permanent magnet always causes the armature to be attracted to the iron core, and even though the spring sheet has a large counter force, but a pressure on the contact point at a normal-close terminal of the product is relatively small. Therefore, load capability of the fixed closed terminal is poor, and the product relay has a poor resistance against impact and vibration.
2. After the coil is excited for reset, the magnetic force of the permanent magnet still generates a strong attraction force to the armature. Therefore, it requires a large reset force to reset the armature to reset to a released state. If the magnetic force does not match the reset force, the coil may require a small setting voltage and a large resetting voltage, or the coil may fail to be reset.